As a nuclear medicine imaging apparatus, Positron Emission computed Tomography (PET) apparatuses are conventionally known. A PET apparatus generates, for example, a function image of a tissue in a human body. More specifically, to perform an image taking process using a PET apparatus, a subject is first dosed with a radiopharmaceutical labeled with a positron emitting nuclide. After that, the positron emitting nuclide that is selectively taken into a body tissue within the subject releases positrons, and the released positrons are coupled with electrons and annihilated. At this time, the positrons release a pair of gamma rays in substantially opposite directions. The PET apparatus detects the gamma rays by using a detector arranged in a ring formation so as to surround the subject and generates simultaneous count information (hereinafter, a “coincidence list”) from the detection result. Further, the PET apparatus performs a reconstructing process through a back-projection process by using the generated coincidence list and generates a PET image.
In this situation, the detector for the PET apparatus includes a scintillator, a photomultiplier tube, and a light guide. An optical coupling between the scintillator and the light guide and an optical coupling between the light guide and the photomultiplier tube are important factors in the performance of the detector. For this reason, materials having similar refractive indexes are usually used at the optical coupling surfaces so as to prevent reflection and scattering of the light. Also, the materials are adhered to each other while ensuring that no air layer or the like is involved.
Generally speaking, however, the optical coupling mentioned above has a possibility of experiencing a detachment due to vibrations during a transport, deteriorations in the course of time, and the like. It is also difficult to visually check for occurrence of optical coupling detachments, because radiating light onto the detector has a possibility of disturbing the mechanical property of the detector. For this reason, a method by which it is possible to check for optical coupling detachments in a nondestructive manner has been in demand.